Optical fibers can be coupled by melting their ends into lenses and placing the lenses in alignment and a predetermined distance apart. Lenses of fairly uniform size and high strength can be formed by placing a pair of electrodes on opposite sides of an optical fiber end portion and establishing an arc between the electrodes that melts the fiber portion between them. The arc can be more closely controlled by repeatedly turning it on and off, and especially by establishing an alternating current, or AC, arc of a high frequency such as 75 kHz.
A low-cost power supply which can generate a relatively high frequency such as 75 kHz of substantial current such as 30 milliamperes at a considerable voltage is a DC source which is switched on and off at the desired frequency. This produces pulses or square waves, which may be amplified by passage through a transformer. The output of such a circuit may be somewhat like a square wave. While a largely square wave at the desired frequency can produce a closely controlled arc, it can result in creation of large undesirable vibrations of the optical fiber. Resonant vibration of the optical fiber, especially of the molten ball of glass as it is hardening, can degrade the quality of the lens. The optical fiber may have a diameter of about 0.005 inch, with the lens being only about 50% greater in diameter, and is subject to resonant vibrations at high frequencies.
Uniformity of lens size can be controlled to a large extent by controlling the voltage across the electrodes and the period during which the arc is maintained. However, fiber heating and consequent lens size and position can be affected by the particular atmospheric conditions.
A system for forming a high frequency arc, which minimized the possibility of creating high frequency resonant vibrations in the optical fiber, with the system being relatively simple and of low cost while closely controlling the melting of the optical fiber, would be of considerable value.